The present invention relates to a personal identification technology for identifying individuals by matching of dermatoglyphic patterns such as fingerprints.
The need for personal identification technologies for identifying specific individuals has increased in various fields involving key or ID-based security and personal verification by passwords or identification codes. Since conventional personal identification techniques tend to make extensive use of specific keys or identification numbers as means for personal identification, they must always be wary of the possibility of duplication or illicit modification, and must also take into consideration the problems which may be caused by the loss of the means of personal identification (such as loss of keys or forgetting of identification numbers). In contrast, the characteristics of fingerprints are highly individual, with no two persons having exactly the same fingerprint, so that in recent years, the use of fingerprints as means of personal identification has aroused considerable interest, and personal identification technologies for identifying a single individual by means of fingerprint matching are being developed for entry into common practice.
Personal identification by means of fingerprint matching is a system, conventionally known as dactyloscopy, whose use has traditionally been reserved for identifying suspects in forensic criminal investigations by the police and similar investigative organizations, and the recent trend toward more mainstream use of such personal identification technologies is based on this past legacy. In fingerprint matching, all fingerprints can be largely divided into five different types of patterns (arch, loop, whorl, variant and scarred), but the simple division into these patterns cannot be considered to be sufficient for unique identification. Therefore, in forensic dactyloscopy, the detailed features or minutiae of fingerprints are taken into consideration to make comparative analyses, and the collecting of such minor features has been held to be essential also to the recent personal identification systems which have been offered as an alternative to keys and passwords in recent years.
As conventional art relating to this type of fingerprint matching, Japanese Patent Application, First Publication No. 2000-148982 discloses a fingerprint matching device for obtaining fingerprint data under constant conditions by fixing the position of the finger to put the fingerprint square against a fingerprint-reading camera. Additionally, Japanese Patent Application, First Publication No. H5-189546 discloses a device for determining whether or not a subject is valid by extracting two types of minutiae, that is, terminal points (where the ridge of a fingerprint ends) and bifurcations (where the ridge of a fingerprint divides), from the fingerprint image.
The fingerprint matching systems currently used by the Japanese police force work under the assumption that the fingerprints will be collected from those left by suspects at a crime scene. Since the latent fingerprints collected at crime scenes can be incomplete and are often only obtained as partial fingerprints (small parts of the fingerprint) corresponding to arbitrary parts of the fingers coming into contact with objects, it is necessary to take a wide range of fingerprints so as to be able to match them against any portion of the fingerprint. Therefore, when fingerprinting suspects or the like, the subject is made to rotate the finger over the paper over a range of at least 180° in order to capture as many features as possible. When performing the match, the gathered latent fingerprints are collated with registered fingerprints using a computer in order to electronically sort them based on the minutiae, and this is followed by a naked-eye comparison.
However, since the registered fingerprints cover a wide area and contain numerous minutiae, the computational power required for collation with latent fingerprints must necessarily be vast. Moreover, the taking of fingerprints by rotation as described above can cause fingerprints to be difficult to reconstruct due to the frequent occurrence of smudging and smearing of the fingerprints when taking the fingerprints (due to the elasticity of the fingerprints). That is, since the shape of a fingerprint depends on the force applied in the vertical and horizontal directions when taking the fingerprint, a latent fingerprint may sometimes not be recognized by electronic sorting to be the same as the registered fingerprint of the same person (the same finger) if there is a difference in the way in which the force is applied. Due to this reason, the above-described sorting by computers involves a large amount of computation and takes a lot of time, while still having relatively low precision during collation (as a result, most matching is actually dependent on human judgment).
Additionally, the personal identification techniques of recent years which are based on forensic fingerprint matching have the similar problems of requiring a lot of processing time yet having low precision, and a solution has been sought. In contrast, the fingerprint matching device disclosed in the above-mentioned Japanese Patent Application, First Publication No. 2000-148982 attempts to control the deformation or displacement of fingerprints by obtaining fingerprint data under identical conditions, but offers no solution for the large processing quantities. Additionally, not only is the structure such as to require a rotary mechanism to rotate the fingerprint-reading camera, but it also reads the finger (fingerprint) with the fingerprint-reading camera with the finger held in the air, and therefore requires a complex image processing capability in order to allow the fingerprint to be obtained as two-dimensional image data that is suitable for making comparisons. On the other hand, since the device disclosed in the above-mentioned Japanese Patent Application, First Publication No. H5-189546 considers only the validity of individual minutiae, the above-described processing time and sorting precision are not affected. Thus, the current personal identification technologies that use fingerprint matching do not offer a complete solution to the large amount of processing required of computers and the inadequacies in matching precision, so that there are no accurate and convenient personal identification systems.